[1] Clarkia biloba is endemic to California, where it is known from the Sierra Nevada foothills; one subspecies can also be found in the San Francisco Bay Area.

[1] As the putative progenitor species of Clarkia lingulata it is often used in examples of evolution outside the usual model of allopatric speciation.

Clarkia biloba is an annual herb producing an erect stem approaching 1 metre (3.3 ft) in maximum height.

The top of the erect stem is occupied by the inflorescence, which bears hanging buds above open flowers.

The pink or red-purple sepals remain fused as the petals spread and emerge from one side of the bud.